The present invention relates to a quantum computing chip, and, more specifically, to the placement of components on a quantum computing chip.
In quantum computing, a circuit is contains many quantum bits (qubits), which are quantum oscillators. This circuit thus comprises the qubits, in addition to resonators and signal ports, formed as a thin film on a substrate. The oscillators (qubits) are connected explicitly by resonator buses in a pattern which is laid out on the supporting substrate surface. When interactions between qubits are controlled, and these interactions only occur in the fashion intended by the layout proscribed by the connecting resonators, the quantum computer will function as intended. However, if additional communication between qubits occurs, due to inadvertent coupling, for example, then the functioning of the quantum computer may not be as designed and calculations may fail. In addition, the qubits can suffer from connection to noise sources which manifest as undesirable perturbations in amplitude and phase (T1 and T2 relaxation). Longer coherence times (larger values for T1 and T2) correspond to a longer time to perform quantum operations before the system decoheres.
Several factors may contribute to crosstalk and to the perturbations in the oscillation which hasten the T1 and T2 relaxation. Signal ports are points on the circuit through which voltage may be applied to drive the circuit and output signals from the circuit are received. The substrate itself may be one source of crosstalk and/or decoherence. The substrate, typically formed of an insulating material with a high dielectric constant, may be viewed as a microwave resonator with chip resonant modes (chip modes) that may be close to the qubit frequency such that they couple with the qubit frequency. The chip modes may also facilitate unwanted interactions or crosstalk between qubits if the chip modes are excited while a qubit is being driven. In addition, the chip modes may cause decoherence (which we call here the Purcell effect or Purcell loss).